I just came back from a trip to Tahoe in my 535i, and the car did kind of well in light snow despite its RWD and all season tires, but it was definitely not confidence inspiring in any shape or form.
Having had an X5 before and having lived in Ontario, Canada for many years prior to moving to sunny California, I would say that an all wheel drive car is better suited for general driving conditions in snowy weather, at least for me that has been the case.
Now a question that should fit well in this thread: for my upcoming weekend trips to Tahoe and occasional snow driving, what are my options? buying a second set of wheels and mounting aggressive snow tires on them? or Perhaps changing the current tires (OEM) to a more snow-friendly all season run-flat tires, if so, which one?